Heard Dr Pace interviewed on NPR and he found that plastic showerheads/ plumbing harbored a significantly higher level of pathogens than metal showerheads/plumbing. The interesting part to me, as an aquarist, is that copper is an effective antipathogen in aquariums, to the point where it can kill not only parasites but also corals and invertebrates. Perhaps copper plumbing is not only efficient, but it also protects our health ?

That is true.
One of the good points of copper.
It's funny because there is a lot of debate over what is best but really the answer is there is no perfect material and when it's invented I'll surly be using it. Really the answer is to select the best material for use in the particular application for best results.

You lost your mind s.l.o.w.l.y...with lead pipe...I just was looking at a leaking lead pipe the other day...I told the guy that the whole line needed to be replaced...he had no Idea that his main supply line was lead...

It's hard to see this as a serious threat, and it is one that can be controlled/reduced. Consider a couple of things for a moment to put the results in perspective:

1. Who puts their face into the initial stream of water from the showerhead? Nobody that I know of (with an asterisk *) Okay, so if the concentration is 100 times higher in that initial rush of water where does most of it end up? Down the drain. So perhaps the level is still elevated by the time the shower taker is actually wetting face and hair, but it is likely to be at worst a few times greater than normal tap water. If so then it is not any more of a threat.

2. There should be several ways of reducing the concentration. One that was already mentioned was using a metal showerhead. But it would also seem that doing the intial warm up of the shower with full hot would also be helpful in chasing out the worst of the nasties. Warming this way is faster and actually uses less water (and perhaps less water heating) because it doesn't waste cold water in the mix. Those who are really paranoid could let it run somewhat longer in hot only mode...

3. Using a non-aerating showerhead should eliminate the worst of the minute suspended droplets that are the real cause for concern.

4. It was the largest municipal systems that had the problems, not smaller systems and wells.

* The two things this does make me wonder about are recirc systems and tub/shower diverters. With both the shower head will have relatively little flow through it before the water reaches temp. (With the tub/shower diverter one is inclined to warm up rapidly through the higher flow tub spout, and do the initial temp setting there.) In those cases one might be more likely to be doused with higher concentration of bacteria.